CN108950581B - Regeneration method of stainless steel mixed pickling waste acid - Google Patents
Regeneration method of stainless steel mixed pickling waste acid Download PDFInfo
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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Abstract
A regeneration method of stainless steel mixed pickling waste acid comprises the following steps: adding an oxidant into the stainless steel mixed pickling waste acid to adjust the oxidation-reduction potential of a waste acid system, wherein the stainless steel mixed pickling waste acid contains nitric acid and hydrofluoric acid; then the obtained mixed solution is reacted under the conditions of heating and pressurizing; and carrying out solid-liquid separation on the slurry formed after the reaction to obtain a regenerated acid solution. According to the invention, metal ions in the waste acid are removed through high-temperature hydrolysis, the regenerated acid liquor is directly returned to the stainless steel washing process, and the metal precipitate is a non-toxic and harmless stable oxide, so that a zero-emission cleaning treatment process is realized.
Description
Technical Field
The invention relates to the technical field of clean recycling of industrial waste acid, in particular to a regeneration method of stainless steel mixed pickling waste acid.
Background
A large amount of inorganic acid washing is required for surface treatment in the rolling process of stainless steel, so that a clean and smooth stainless steel surface is obtained. In order to enhance the pickling effect, the pickling process of the stainless steel surface generally comprises a mixed pickling process of nitric acid and hydrofluoric acid. Part of iron and a small amount of elements such as nickel, chromium and manganese in the stainless steel are also partially dissolved into the pickling solution in the pickling process. When the metal element accumulation reaches a certain concentration, the pickling solution loses the washing effect and generates a large amount of washing waste acid. The waste acid contains a large amount of iron which mainly exists in the forms of Fe (III) and Fe (II), and the waste acid also contains trace elements such as Ni, Cr, Mn and the like according to different types of stainless steel.
At present, the pickling solution is usually treated by a neutralization and precipitation method, and a large amount of toxic waste residues are generated to harm the environment. With the increasing demand for environmental protection, it has become increasingly difficult to neutralize the discharge of waste water and waste residues, and other methods of recovering and disposing of waste acids have been developed. For example, some enterprises have introduced foreign Ruthner spray roasting processes for recovering acids and metals, where the spent acid is preconcentrated and the metals in the spent liquor are hydrolyzed by high temperature roasting, which can recover 97% HF and 60% -70% HNO3. However, the process requires procedures of predrying, dehydration, high-temperature roasting, acid recovery in gas phase, nitrogen oxide absorption, catalytic conversion and the like, and has the disadvantages of high technical control difficulty, high energy consumption and easy atmospheric pollution.
For another example, the resin adsorption method is adopted to recover the free acid in the waste acid, so that a certain range of industrial application is achieved, the resin is used for selectively adsorbing the free acid in the waste liquid to be separated from the metal nitrate and the fluoride, and more than 94 percent of free HNO can be recovered3And more than 70 percent of free HF, the removal rate of metal ions can reach more than 70 percent, and the recovered acid can be recycledThe ring is reused. However, the metal salt solution after acid recovery in the process still needs neutralization treatment, toxic waste residues are still generated, a large amount of waste liquid is still discharged after neutralization, and in addition, the recovered acid has low concentration and can be recycled after concentrated acid is supplemented.
For another example, the volatile HNO in the mixed waste acid can be replaced by the non-volatile sulfuric acid under reduced pressure at 50-70 DEG C3And HF, post-absorption HNO3The recovery rate of HF and H in the solution reaches over 90 percent2SO4The recovery rate reaches more than 80 percent by adopting a resin adsorption method for recovery. The residual waste acid solution is treated by a fractional precipitation method, firstly, lime milk is precipitated at pH3.0 to obtain calcium sulfate neutralization slag without heavy metal, the calcium sulfate neutralization slag can be used as building materials, then, sodium carbonate and sodium sulfide are adopted to completely precipitate heavy metal ions in the waste liquid, the precipitate can be used as a resource to extract metal, and the neutralized waste water reaches the discharge standard. The method can recycle most of high-value HNO3And HF, the metal can be recycled, and the discharge of toxic solid waste is reduced. However, the method generates a large amount of waste residues, is difficult to be reused, and has large waste liquid generation amount, complex process and high cost because the method comprises a plurality of washing processes.
As another example, HF and NO contained in the product obtained by decomposition may be treatedx、HNO3The flue gas is subjected to acid absorption, washing by a washing tower and NOxOxidation conversion, condensation absorption and catalytic denitration to ensure HNO3The recovery rate is improved to over 75 percent, and NO is discharged from waste gasxReduced to 50mg/m3. Although the method improves the efficiency of the existing spray roasting method and reduces the pollution of waste gas, the method does not solve the defects of high energy consumption, low acid yield, complex process and the like.
In addition, the stainless steel washing waste acid can be treated by an electrolytic method and a membrane permeation method, the acid and metal in the washing waste liquid can be recovered, the method is simple and short in flow, but the method is complex in equipment, difficult in process control, incapable of recycling the acid, and incapable of solving the problem of waste residue and waste liquid discharge.
In conclusion, the existing treatment of the stainless steel mixed pickling waste acid still has the problems of large amount of waste residues and waste liquid, complex treatment process, high cost and the like.
Disclosure of Invention
In view of the above, the main object of the present invention is to provide a method for regenerating waste acid from mixed pickling of stainless steel, which realizes regeneration cycle of mixed acid by metal ion hydrolysis, thereby solving at least one of the above mentioned technical problems.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a regeneration method of stainless steel mixed pickling waste acid comprises the following steps:
(1) adding an oxidant into the stainless steel mixed pickling waste acid to adjust the oxidation-reduction potential of a waste acid system, wherein the stainless steel mixed pickling waste acid contains nitric acid and hydrofluoric acid;
(2) reacting the mixed solution obtained in the step (1) under the conditions of heating and pressurizing;
(3) and (3) carrying out solid-liquid separation on the slurry formed after the reaction in the step (2) to obtain a regenerated acid solution.
The stainless steel mixed pickling waste acid takes nitric acid and hydrofluoric acid as main acid components, and can be mixed with a small amount of other acids, such as sulfuric acid, phosphoric acid and/or hydrochloric acid.
Wherein the total concentration of free acid in the stainless steel mixed acid is H+The concentration is 0.5-5 mol/L, and the total concentration of mixed sulfuric acid, phosphoric acid or hydrochloric acid is 0-0.5 mol/L.
The stainless steel mixed pickling waste acid also comprises metal ions, and the metal ions take iron ions as main components.
The metal ions further comprise at least one of nickel ions, manganese ions and chromium ions, wherein the total concentration of the metal ions is 15-100 g/L, and the total concentration of the nickel ions, the manganese ions and the chromium ions is 0-50 g/L.
Wherein the oxidant added in the step (1) is selected from potassium permanganate, hypochlorous acid, perchloric acid or hydrogen peroxide.
And adjusting the oxidation-reduction potential in the stainless steel mixed pickling waste acid to be 500-1300 mV after adding an oxidant.
And (2) adding seed crystals into the mixed solution obtained in the step (1), wherein the seed crystals are preferably alpha-iron oxide, and the addition amount of the seed crystals is 0.1-2% of the iron content in the waste acid by mass.
Wherein, in the step (2), the reaction temperature is 180-250 ℃, the reaction pressure is 1.0-4.0 MPa, and the reaction time is 1-24 h.
Wherein, the regenerated acid solution obtained in the step (4) is used for mixed pickling of stainless steel.
Based on the technical scheme, the invention has the beneficial effects that:
(1) the metal ions in the stainless steel mixed pickling waste liquid are removed through high-temperature hydrolysis, the acid in the waste liquid is regenerated and directly returned to the stainless steel washing process, and the metal precipitate is a non-toxic and harmless stable oxide and can be used as a raw material to be utilized, so that the zero-emission cleaning treatment process is realized.
(2) Meanwhile, the process equipment is simple, the implementation is easy, the treatment cost is low, the consumption of raw materials is reduced by recycling acid and metal, and the additional value of the treatment process is increased.
(3) The method can adjust the precipitation rate of metal ions by controlling the oxidation-reduction potential, temperature and pressure, so that the concentration of the metal ions in the regenerated acid solution can be controllably adjusted, and a higher washing effect is achieved, and therefore the method is strong in controllability.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments.
The invention adopts a high-temperature hydrolysis method to the stainless steel mixed pickling waste acid to hydrolyze metal ions in the waste acid to generate hydroxide, and then the hydroxide is transformed at high temperature and high pressure to generate insoluble metal oxide. When metal ions, especially iron ions, exist in a low valence state, an oxidant is added, the oxidation-reduction potential in the solution is controlled to be more than 500mV, and the low valence state Fe is converted into high valence state Fe. The main chemical reactions are shown as formulas (1) and (2).
M++NO3-+F-+H2O→M(OH)n+HNO3+HF； (1)
M(OH)n→M2On； (2)
The metal ion precipitate is removed by filtration, and simultaneously nitrate radical and hydrofluoric acid radical combined with salt and hydrogen ions generated by hydrolysis form acid, and the acid in the waste liquid is regenerated. The method of the invention not only can form and exist metal as stable oxide, is nontoxic and harmless, can be used as a raw material for steelmaking, but also can regenerate and recycle acid. The method has the advantages of simple required equipment, easy implementation and elimination of the discharge pollution of waste residues and waste water.
Specifically, the invention provides a regeneration method of stainless steel mixed pickling waste acid, which comprises the following steps:
(1) adding an oxidant into the mixed pickling waste acid of the stainless steel to adjust the oxidation-reduction potential of a waste acid system;
(2) reacting the mixed solution obtained in the step (1) under the conditions of heating and pressurizing;
(3) and (3) carrying out solid-liquid separation on the slurry formed in the step (2) to obtain a regenerated acid solution.
Wherein, the waste acid generated by the mixed pickling of the stainless steel mainly contains nitric acid and hydrofluoric acid, but is not limited to the nitric acid and the hydrofluoric acid, and the mixed waste acid can also contain a certain amount of sulfuric acid, phosphoric acid, hydrochloric acid and the like according to different washing processes, and the total concentration of free acid in the waste acid (as H)+Concentration meter) is 0.5-5 mol/L, wherein the total concentration of the sulfuric acid, the phosphoric acid and the hydrochloric acid is 0-0.5 mol/L.
The waste acid contains metal ions, the metal ions are mainly iron ions, and can also contain metal ions such as nickel, manganese, chromium and the like, the total concentration of the metal ions is 15-100 g/L, and the total concentration of trace metal ions such as nickel, manganese, chromium and the like is 0-50 g/L.
When the metal ions in the waste acid are in a low valence state, an oxidant can be added to adjust the oxidation-reduction potential, preferably potassium permanganate, hypochlorous acid, perchloric acid or hydrogen peroxide, so that the oxidation-reduction potential in the waste acid is controlled to be 500-1300 mV.
Wherein, the method also comprises a step of adding seed crystals to the mixed liquid obtained in the step (1) before the step (2), and the added seed crystals are preferably alpha-Fe2O3The added mass is 0.1-2% of the iron content in the waste acid.
Wherein the reaction temperature is 180-250 ℃; the reaction pressure is 1.0-4.0 MPa; the heat preservation time range is 1-24 h, and preferably 8-12 h. The metal ions are hydrolyzed under the above conditions to thereby form a metal oxide precipitate.
Wherein, the solid-liquid separation is carried out on the formed slurry after the metal ions are hydrolyzed, and the acid solution after the separation returns to the stainless steel washing section for recycling.
The following examples are presented to further illustrate the technical solution of the present invention:
example 1
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 36 g/L; fe (II), 12 g/L; HNO30.6 mol/L; HF, 0.5 mol/L. Waste acid is put into a high-temperature high-pressure reaction kettle, and 15mL of 30% H is added2O2The redox potential of the solution was controlled to 500 mV. Keeping the temperature at 180 ℃ under the pressure of 1.0MPa for 24h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 21.5g of solid, wherein the total precipitation rate of iron is 62.9%. The components of the acid solution after treatment are as follows: fe, 17.8 g/L; HNO30.5 mol/L; HF, 0.4 mol/L. The acid solution after solid-liquid separation can be recycled for mixed pickling of stainless steel.
Example 2
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 36 g/L; fe (II), 12 g/L; HNO30.6 mol/L; HF, 0.5 mol/L. Waste acid is put into a high-temperature high-pressure reaction kettle, and 20mL of 30% H is added2O2Controlling the oxidation-reduction potential of the solution to be 550mV, and then adding 0.05g of alpha-Fe2O3. Keeping the temperature at 180 ℃ under the pressure of 1.0MPa for 12h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 23.0g of solid, wherein the total precipitation rate of iron is 66.4%. The components of the acid solution after treatment are as follows: fe, 16.1 g/L; HNO30.5 mol/L; HF, 0.4 mol/L. The acid solution after solid-liquid separation can be recycled for mixed pickling of stainless steel.
Example 3
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 36 g/L; fe (II), 12 g/L; HNO30.6 mol/L; HF, 0.5 mol/L. Waste acid is put into a high-temperature high-pressure reaction kettle, and 20mL of 30% H is added2O2Controlling the oxidation-reduction potential of the solution to be 550mV, and then adding 0.48g of alpha-Fe2O3. Keeping the temperature at 180 ℃ under the pressure of 1.0MPa for 12h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 27.0g of solid, wherein the total precipitation rate of iron is 76.2%. The components of the acid solution after treatment are as follows: fe, 11.4 g/L; HNO30.5 mol/L; HF, 0.4 mol/L. The acid solution after solid-liquid separation can be recycled for mixed pickling of stainless steel.
Example 4
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 75 g/L; HNO31.5 mol/L; HF, 1.0 mol/L. Waste acid is put into a high-temperature high-pressure reaction kettle, and 25mL of 30% H is added2O2Controlling the oxidation-reduction potential of the solution to 800mV, and then adding 0.7g of alpha-Fe2O3. Keeping the temperature at 220 ℃ and 2.3MPa for 12h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 51g of solid, wherein the total precipitation rate of iron is 95.2%. The components of the acid solution after treatment are as follows: fe, 3.5 g/L; HNO31.4 mol/L; HF, 0.9 mol/L. The acid solution after solid-liquid separation can be used for mixed pickling of stainless steel.
Example 5
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 50 g/L; HNO32.5 mol/L; HF, 0.7 mol/L. Putting waste acid into a high-temperature and high-pressure reaction kettle, adding 25mL of hypochlorous acid, controlling the oxidation-reduction potential of the solution to be 750mV, and then adding 0.5g of alpha-Fe2O3. Keeping the temperature at 220 ℃ under 2.3MPa for 12h to obtain slurry, performing vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 27g of solid, wherein the total precipitation rate of iron is 80.3%. The acid solution after hydrolysis comprises the following components: fe, 9.5 g/L; HNO32.1 mol/L; HF, 0.6 mol/L. Solid-liquidThe separated acid solution can be used for mixed pickling of stainless steel.
Example 6
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 34 g/L; HNO3，3mol/L；HF，1.3mol/L；H2SO40.2 mol/L. Putting waste acid into a high-temperature and high-pressure reaction kettle, adding 25mL perchloric acid, controlling the oxidation-reduction potential of the solution to 700mV, and then adding 0.5g alpha-Fe2O3. Keeping the temperature at 240 ℃ and 3.4MPa for 21h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 19.6g of solid, wherein the total precipitation rate of iron is 79.6%. The acid solution after hydrolysis comprises the following components: fe, 6.9 g/L; HNO3，2.4mol/L；HF，0.8mol/L；H2SO40.16 mol/L. The acid solution after solid-liquid separation can be used for mixed pickling of stainless steel.
Example 7
The 500mL of stainless steel washing mixed waste acid comprises the following components: fe (III), 34 g/L; ni (II), 1.0 g/L; mn (II)1.2 g/L; HNO3，3mol/L；HF，1.3mol/L；H2SO40.2 mol/L. Putting waste acid into a high-temperature and high-pressure reaction kettle, adding 25mL perchloric acid, controlling the oxidation-reduction potential of the solution to 700mV, and then adding 0.5g alpha-Fe2O3. Keeping the temperature at 240 ℃ and 3.4MPa for 21h to obtain slurry, carrying out vacuum filtration, and drying the precipitate at 100 ℃ for 12h to obtain 19.8g of solid, wherein the total precipitation rate of iron is 79.6%, the precipitation rate of nickel is 80.1%, and the precipitation rate of manganese is 48.2%. The acid solution after hydrolysis comprises the following components: fe, 6.9 g/L; ni, 0.2 g/L; mn, 0.62 g/L; HNO3，2.4mol/L；HF，0.8mol/L；H2SO40.16 mol/L. The acid solution after solid-liquid separation can be used for mixed pickling of stainless steel.
In conclusion, the invention controls the oxidation-reduction potential of the stainless steel mixed pickling waste acid, and then hydrolyzes metal ions and converts the metal ions into stable oxide precipitates under the conditions of high temperature and high pressure to obtain the acid solution which can be recycled, thereby eliminating the discharge pollution of waste residues and waste water, and the method is simple and easy to implement.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A regeneration method of stainless steel mixed pickling waste acid comprises the following steps:
(1) adding an oxidant into the stainless steel mixed pickling waste acid to adjust the oxidation-reduction potential of a waste acid system to be 500-1300 mV, wherein the stainless steel mixed pickling waste acid contains nitric acid and hydrofluoric acid, the nitric acid and the hydrofluoric acid are used as main acid components, and the total concentration of free acid in the stainless steel mixed pickling waste acid is H+The concentration is 0.5-5 mol/L, the stainless steel mixed pickling waste acid also contains metal ions, and the total concentration of the metal ions is 15-100 g/L;
(2) reacting the mixed solution obtained in the step (1) under the conditions of heating and pressurizing, wherein the reaction temperature is 180-250 ℃, and the reaction pressure is 1.0-4.0 MPa;
(3) performing solid-liquid separation on the slurry formed after the reaction in the step (2) to obtain a regenerated acid solution, wherein the regenerated acid solution comprises nitric acid and hydrofluoric acid;
(4) and (4) applying the regenerated acid solution obtained in the step (3) to mixed pickling of stainless steel.
2. The method of regenerating stainless steel mixed pickling waste acid as claimed in claim 1, wherein the stainless steel mixed pickling waste acid is further mixed with other acids, the other acids comprising at least one of sulfuric acid, phosphoric acid and hydrochloric acid.
3. The regeneration method of the waste acid generated in the mixed pickling of the stainless steel according to claim 2, wherein the total concentration of sulfuric acid, phosphoric acid or hydrochloric acid mixed in the mixed acid of the stainless steel is 0-0.5 mol/L.
4. The method for regenerating waste acid from mixed pickling of stainless steel according to claim 1, wherein the metal ions are mainly iron ions.
5. The regeneration method of waste acid from mixed pickling of stainless steel according to claim 4, wherein the metal ions further comprise at least one of nickel ions, manganese ions and chromium ions, and the total concentration of the nickel ions, the manganese ions and the chromium ions is 0-50 g/L.
6. The regeneration method of waste acid from mixed pickling of stainless steel according to claim 1, wherein the oxidant added in step (1) is selected from potassium permanganate, hypochlorous acid, perchloric acid or hydrogen peroxide.
7. The regeneration method of the waste acid from mixed pickling of stainless steel according to claim 1, further comprising a step of adding seed crystals to the mixed solution obtained in step (1) before step (2), wherein the seed crystals are preferably alpha-iron oxide, and the addition amount is 0.1-2% of the iron content in the waste acid by mass.
8. The regeneration method of the waste acid from mixed pickling of stainless steel according to claim 1, wherein the reaction time in step (2) is 1-24 h.
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